As the wind acts on a solar tracking photovoltaic (PV) array or other mechanically driven positioning systems exposed to outdoor environmental forces, it causes positive and negative pressures on the array which may act independently, cumulatively, or differentially. These wind forces are commonly categorized as drag, uplift, downforce and hinge moment about the rotational axis. The wind forces vary depending upon the wind speed, direction and rotational tracking angle of the array. These forces are also usually greater on the outer structures in a large array field.
Typically, in the case of single axis solar tracking systems, the lift and drag induced on the tracked array or other mechanical system are resisted at multiple points within the structure. However, as evidenced by existing systems, the hinge moment typically is resisted at a single point. The resulting torsional forces applied to relatively long torsion tubes or other beam configurations may be large and tend to interact with the torsional flexibility of the tracker structure. Counteracting the high hinge moment forces at a single point in the structure requires sufficiently strong torsional members to resist both the high combined torque and the beam loads of the system without excess flexibility. The hinge moment forces may present as a static force or sometimes dynamic force known as torsional divergence. If the structural system of the tracker is flexible in its design, and is torsionally restrained at a single point, torsional divergence and other dynamic forces may occur that have the potential to substantially increase the loading on the structure. It is therefore structurally advantageous to minimize the flexibility of the tracker structure to reduce or eliminate the wind interactions that may cause these dynamic forces.
Accordingly, there is a need for a mechanism to reduce the peak hinge moment force that a tracking system will be exposed to and/or allow the system to resist the moment forces at multiple points, thereby minimizing or effectively eliminating the dynamic/harmonic forces the structure is exposed to. Minimizing torsion in the structure increases the beam load capability of the relevant structural members since the combination load of the torsion and beam loading is less. By limiting the peak torsion force and then providing a means to resist a lower maximum torsion force at multiple points along the structure, lighter structural components may be incorporated to lower the material weight and cost of solar tracker systems.